Field of the Invention
The present invention relates to devices used for hydrating and slaking lime to produce hydrated lime such as is used in soil stabilization projects.
The conversion of unhydrated quick lime, CaO, to lime hydrate, Ca(OH).sub.2, is referred to as "hydration" or "slaking", depending upon the amount of excess water utilized in the process. Often in the art "slaking" is used to refer to a process utilizing a relatively large amount of water to produce a product slurry, whereas "hydration" describes a process wherein only sufficient water is used; however, for the purposes of this disclosure, the terms "hydration" and "slaking" are used interchangeably.
At the present time, hydrated lime is used in various soil stabilization applications, such as highway road bed stabilization. In a typical application, one or more large mixing tanks, i.e., 24,000 gallons capacity, are hauled to the job site on trucks. Usually at least two mixing tanks are hauled to the job site and connected to an available water source, such as a fire hydrant. The separate mixing tanks are connected by separate lines to a common holding tank. One or more discharge lines from the holding tank are used to fill slurry trucks which then haul the hydrated lime to the work area and spread the lime.
Where separate, batch mixing tanks are used, each tank must first be supplied with 6 to 8 feet of water or approximately 3/4 full, which can take one to one and one half hours in the case of a 24,000 gallon tank. As one of the tanks begins to fill with water, quick lime is delivered to the job site in trucks and added to one of the tanks. A stirrer in the mixing tank agitates the lime and water mixture and a heat of hydration is given off which ultimately raises the water temperature to about 140 degrees F. In attempting to control the reaction, four to five tons of quick lime are typically added to a single mixing tank and agitated. Once the water temperature reaches 140-160 degrees F. the remainder of the quick lime is added to the mixing tank. Once the hydration reaction has run its course, the slurry is passed through a discharge line into the holding tank and from the holding tank into waiting slurry trucks. While the reaction is occurring in one mixing tank, another operator refills the second mixing tank with fresh water. By staggering the refilling operation and the hydration reaction steps between two mixing tanks, some time is saved in getting the lime slurry to the slurry trucks.
Existing lime hydration systems for soil stabilization projects suffer from a number of disadvantages. The use of multiple, large capacity tanks is very expensive. If a water line is not available as the source of fresh water, water must also be hauled to the job site. Even by using a plurality of mixing tanks and alternately switching between tanks, it is extremely difficult to continuously supply slurry to the waiting slurry trucks. It is not possible to spread and leave hydrated lime exposed to the atmosphere for more than about 24 hours without oxidation of the lime particles occurring and resulting wasted product. Since it is difficult to continuously supply slurry with existing systems, it is often necessary to prepare a sufficient quantity of slurry beforehand and store the slurry overnight in storage tanks.
There exists a need, therefore, for a lime hydrating device of the type used to supply hydrated lime in soil stabilization projects which can be operated to continuously produce a slurry product without intermittant delays.
There exists a need for such a device which is mobile and can be easily transported from one job site to another.
There exists a need for such a device which utilizes the heat given off by the hydration reaction to more completely effect the complete conversion of the quick lime entering the device into hydrated lime.
The above objects are accomplished in the device of the invention, as will be described.